High-pressure metal vapor discharge lamps, particularly sodium vapor lamps with hermetic seal

ABSTRACT

An annular member of ceramic is fitted into each end of the cylindrical arc tube of refractory light-transmissive material such as polycrystalline alumina and connected to the arc tube by sintering or by a glass or metal solder and having a hollow lead sealed internally thereof; the arrangement and the dimensions are so selected that the point of sealing of the annular member to the arc tube is protected from corrosion and a bubble-free solder seal is achieved.

Unite States 'ate nt [191 Ptaue Aug. 27, 1974 HIGH-PRESSURE METAL VAPOR DISCHARGE LAMPS, PARTICULARLY SODIUM VAPOR LAMPS WITH HETIC SEAL Inventor: Johannes Pfaue, Berlin, Germany Assigne'i Patent-Treuhand-Gesellschaft fur Elektrische Gluhlampen GmbH,

Munich, Germany 1 Filed: Feb. 27, 1973 Appl. No.: 336,371

Foreign Application Priority Data Mar. 1, 1972 Germany 2209848 US. Cl 313/217, 313/219, 313/220, 313/227, 313/289 [58] Field of Search 313/217, 219, 220, 221, 313/225, 227-229, 252, 253, 256, 286, 288,

Int. Cl H01j 17/18, HOlj 61/36 [56] References Cited UNITED STATES PATENTS 3,450,924 6/1969 Knochel et al.... 313/220 3,660,71 l 5/1972 Stanyon et a1. 313/220 3,716,743 2/1973 Mizuno et al 313/220 Primary Examiner.1ohn Kominski Assistant Examiner-Siegfried H. Grimm Attorney, Agent, or FirmFlynn & Frishauf 9 Claims, 1 Drawing Figure HIGH-PRESSURE METAL VAPOR DISCHARGE LAMPS, PARTHCULARLY SODIUM VAPOR LAMPS WTTH HERMETIC SEAL Cross reference to related application: US. Patent Application Ser. No. 336,368 filed Feb. 27, 1973.

The invention relates to high pressure metal vapor discharge lamps and more particularly to hermetic seals in high pressure sodium vapor discharge lamps.

High pressure discharge lamps usually have a cylindrical discharge vessel, a so-called arc tube, of refractory, light-transmissive material, preferably of polycrystalline alumina. One of the structural components of the seal is an annular member of ceramics which fits into the end of the arc tube and has a hollow lead, preferably of niobium, sealed internally thereof. The annular member is connected to the arc tube by sintering or by a glass or metal solder.

It is already known to seal the ends of the arc tube by means of one annular ceramic member, each (see German Pat. No. 1,471,379). Furthermore, it is known to provide an additional annular member which is pressed, like a lid, from outside against the ends of the discharge tube (see US. Pat. No. 3,607,437). The service life of such seals is uncertain depending on the material used and the sealing techniques applied. After longer periods of operation, strains may occur in the arc tube which lead to cracks. Moreover, the sealing operation is usually a complicated process step which is expensive.

The invention, in general, relates to high pressure metal vapor discharge lamps, more particularly high pressure sodium vapor discharge lamps with hermetic seals. Such lamps have a cylindrical discharge vessel, a so-called arc tube of refractory, light-transmissive material, preferably of polycrystalline alumina. One of the structural components is an annular member of ceramics which fits into the end of the arc tube, having a hollow lead preferably of niobium sealed internally thereof, and connected to the arc tube by sintering or by a glass or metal solder.

It is an object of the present invention to provide an improved hermetically sealed arc tube for such lamps.

SUBJECT MATTER OF THE INVENTION Briefly, the length of the annular member is at least half and not more than three times its largest outer diameter; the inner diameter of the annular member is constant at least across that section to which the hollow lead is sealed; and the outer diameter of the end facing the discharge space is reduced across not more than two thirds of the length of the annular member.

It is advantageous if the inner diameter of the free end of the annular member facing the discharge space varies relative to that section to which the hollow lead is sealed, and the outer diameter of the end of the annular member facing the discharge space is reduced at most across half the length of said member. It is suitable to provide in the external cylindrical section of the annular member at least one, better still two annular grooves. The end of the annular member of reduced outer diameter is not sealed to the arc tube.

The invention will be described by way of example with reference to the accompanying drawings, wherein the single FIGURE is a longitudinal cross section embodiment. Both ends of the lamp may be sealed simultaneously; in the drawing, the end A of the lamp is shown in a condition prior to sealing while end B is shown in sealed condition in order to illustrate the invention.

l designates the arc tube of polycrystalline alumina. The annular member 2 is made of the same material and encompasses the hollow lead 3, 3' respectively of niobium. The end portion of the lamp is not only provided with the member 2 but in addition with an end cap 5 of niobium to which the lead 3, 3 respectively is connected by means of solder 4. Interposed between the front surface of annular member 2 and end cap 5 is a ring 6 of glass solder. Glass solder 6 which melts during sealing, flows into the existing cavities and hermetically seals member 2 to are tube 1 and lead 3, 3', and to end cap 5 so that a hermetic seal is formed at the end of the arc tube between annular member 2 and the other lamp parts. In an example of a 400 W Xenon lamp, member 2 has a length of 8 mm; its largest outer diameter is about 7.8 mm. The annular grooves 7 provided in the external cylindrical section of member 2 have a depth of 1 mm and are formed so that the mutual spacing of grooves and the spacing from groove to border of the cylindrical section of member 2 is in each case 1 mm. This configuration of member 2 ensures that possibly existing gas bubbles are pressed into the grooves during sealing so that a bubblefree solder seal will result.

The end of member 2 is tapered towards the lamp interior while the inner diameter is maintained constant. The inner diameter of member 2 may, however, be

constant merely in the region of that section to which the lead 3, 3', respectively, is sealed, and be variable towards the end facing the lamp interior. The taper of the outer diameter extends across 3 mm of length of member 2 so that end 8 freely projects into the discharge space. This shape of the end of the annular member also prevents establishment of an electrical connection between seal 9 and lead 3, 3 respectively by condensed residues of the metal used as the fill, and that the are, after ignition, initially strikes in this place until the electrical connection is interrupted, that is, when the metal film has vaporized and the arc flashed over to the electrode.

The lead 3, 3 respectively carries core rod 10 and filament coil 11. Lead 3 is in communication with the interior of the arc tube via a small opening 12. The hollow lead 3 is closed off at its outer enlarged end 13 by a metal lid 14 save for a small aperture 15. Aperture 15 is closed by small metal plates 16 which are melted by resistance heating. The enlarged portion 13 of lead 3 contains sodium amalgam 17 and a filament coil 18 with capillary interstices which provide a continuous measured supply of the sodium to the lamp interior. The hollow lead 3 is closed off from the lamp interior by three stacked discs 19 peripherally fused to the lead, with a titanium disc of 0.2 mm thickness sandwiched between two discs of niobium of 0.1 mm thickness. Metal support 20 welded to the end of lead 3, 3' proximate the electrode is used for support of ring 2 prior to sealing.

The lamp has a wattage input of 400 W and is filled with xenon of 20 torr as the basic gas and with mgs of sodium amalgam. The diameter of the arc tube is 7.9 mm, the electrode spacing 84 mm.

I claim:

sel (1) of refractory, light-transmissive material and structural components associated therewith wherein one of the structural components is an annular member (2) of ceramic which fits into the end of the vessel (1) and having a hollow lead (3, 3) sealed inside the annular member (2), seal means (9) sealing the annular member (2) within the vessel to connect said member to the vessel (1), wherein the length of the annular member (2) is at least half and not more than three times its largest outer diameter;

the inner diameter of the annular member (2) is constant at least along that section to which the hollow lead (3, 3) is sealed;

the outer diameter of the end of the annular member (2) facing the discharge space is reduced over a length not more than two thirds of the length of the annular member (2); and

the seal (9) between the vessel (1) and the ceramic annular member (2) extends only over a portion of the length of the annular member which projects internally of the vessel (1).

2. Lamp according to claim 1, wherein the inner diameter of the internally projecting end of the annular member facing the discharge space varies relative to that section to which the hollow lead is sealed.

3. Lamp according to claim 1, wherein the outer diameter of the end of the annular member facing the discharge space is reduced at most along half the length of said member.

4. Lamp according to claim I, wherein the annular member includes a cylindrical section, and at least one annular groove is provided in the outside circumference of the cylindrical section of the annular member.

5. Lamp according to claim 1, wherein the annular member includes a cylindrical section having two grooves formed at the outside circumference.

6. Lamp according to claim 1, wherein the end portion of the annular member which projects internally of the vessel free from the seal comprises the portion of reduced outer diameter.

7. Lamp according to claim 1, wherein the lamp is a high-pressure sodium vapor discharge lamp; the discharge vessel is of polycrystalline alumina; and the hollow lead is of niobium.

8. Lamp according to claim 7, wherein the inner diameter of the internally projecting end of the annular member facing the discharge space varies relative to that section to which the hollow lead is sealed, and the outer diameter of the end of the annular member facing the discharge space is reduced at most across half the length of said member.

9. Lamp according to claim 7, wherein the annular member includes a cylindrical section, and at least one annular groove is provided in the outside circumference of the cylindrical section of the annular member. l 

1. A hermetically sealed high-pressure metal vapor discharge lamp comprising a cylindrical discharge vessel (1) of refractory, light-transmissive material anD structural components associated therewith wherein one of the structural components is an annular member (2) of ceramic which fits into the end of the vessel (1) and having a hollow lead (3, 3'') sealed inside the annular member (2), seal means (9) sealing the annular member (2) within the vessel to connect said member to the vessel (1), wherein the length of the annular member (2) is at least half and not more than three times its largest outer diameter; the inner diameter of the annular member (2) is constant at least along that section to which the hollow lead (3, 3'') is sealed; the outer diameter of the end of the annular member (2) facing the discharge space is reduced over a length not more than two thirds of the length of the annular member (2); and the seal (9) between the vessel (1) and the ceramic annular member (2) extends only over a portion of the length of the annular member which projects internally of the vessel (1).
 2. Lamp according to claim 1, wherein the inner diameter of the internally projecting end of the annular member facing the discharge space varies relative to that section to which the hollow lead is sealed.
 3. Lamp according to claim 1, wherein the outer diameter of the end of the annular member facing the discharge space is reduced at most along half the length of said member.
 4. Lamp according to claim 1, wherein the annular member includes a cylindrical section, and at least one annular groove is provided in the outside circumference of the cylindrical section of the annular member.
 5. Lamp according to claim 1, wherein the annular member includes a cylindrical section having two grooves formed at the outside circumference.
 6. Lamp according to claim 1, wherein the end portion of the annular member which projects internally of the vessel free from the seal comprises the portion of reduced outer diameter.
 7. Lamp according to claim 1, wherein the lamp is a high-pressure sodium vapor discharge lamp; the discharge vessel is of polycrystalline alumina; and the hollow lead is of niobium.
 8. Lamp according to claim 7, wherein the inner diameter of the internally projecting end of the annular member facing the discharge space varies relative to that section to which the hollow lead is sealed, and the outer diameter of the end of the annular member facing the discharge space is reduced at most across half the length of said member.
 9. Lamp according to claim 7, wherein the annular member includes a cylindrical section, and at least one annular groove is provided in the outside circumference of the cylindrical section of the annular member. 